A problem with conventional building construction, especially residential buildings, is that moisture tends to condense in the space between the exterior sheathing and the interior wall. This can occur whenever the surfaces of the exterior sheathing are at or below the dew point temperature of the air between the exterior sheathing and the interior wall. It is believed that the improved air tight sealing techniques currently used in the building construction industry reduce the air exchange rate both within the living space of the building and within spaces between exterior sheathing and interior walls. While the improved air tightness of modern buildings results in energy savings, and lower heating and air conditioning costs, condensation between exterior sheathing and interior walls can promote the growth of biological pollutants such as mold, mildew and bacteria.
As is evident from recent publications and events, the proliferation of litigation, insurance claims and consumer concern relating to health issues associated with mold and other biological pollutants have attracted the attention of the residential construction industry. However, current efforts to eliminate and/or reduce mold growth in buildings have focused on preventing water infiltration such as through basement walls, detecting and eliminating plumbing leaks, exhausting air from showers, baths, kitchens, and other moisture generating areas to the outside of the building, and automating dehumidification and/or regulation of air exchange rates based on relative humidity in the living space. These efforts provide beneficial results. However, they do not eliminate or significantly reduce the potential for condensation between exterior sheathing and interior walls. Regulating conditions within the interior living spaces of a building does not prevent air trapped between exterior sheathing and interior walls from contacting surfaces at or below the dew point temperature of the trapped air, and therefore does not prevent condensation on these cool surfaces. Such condensation can facilitate mold growth since mold spores are relatively ubiquitous and can thrive in many wet or damp environments provided they have an adequate food source. Unfortunately, many building materials contain organic materials that molds may use as a source of food. For example, molds can grow on wood products, paper, wallboard and painted surfaces if there is adequate moisture. It is generally well accepted that the only practical way of preventing mold growth in buildings is to prevent water leaks and condensation from accumulating on building materials and/or other materials that can provide nourishment to the molds, since it is practically impossible to prevent the microscopic mold spores from contacting building materials and/or eliminate food sources from building materials.
Elimination of mold growth in buildings is extremely important. Even relatively small amounts of mold can release toxic chemicals that cause dry coughs, runny noise, rashes and fatigue. Sensitive individuals may experience more serious health problems, such as headache, nosebleed, dizziness, allergic reactions, asthma and/or other respiratory problems. High levels of mold contamination can cause very serious chronic and acute health problems such as neurological disorders, brain damage, autonomic dysfunction, hypotension and/or cancer. Accordingly, building techniques and structures that prevent condensation while achieving good energy efficiency are needed.
Another problem that frequently occurs in residential buildings, especially in the vicinity of a sky light or roof window, is the formation of ice dams. Ice dams can form on sloped roofs down slope of a hot spot on the roof. Heat from a hot spot on the roof can cause snow to temporarily melt and re-solidify at a down slope colder spot on the roof, thereby forming an ice dam which can cause water to pool up slope of the ice dam. Roofs are typically designed to shed water by allowing it to cascade down the sloped roof from one roof tile to an adjacent roof tile until it falls off the edge of a roof, such as into a gutter or directly onto the ground. However, sloped residential roofs are not typically watertight. As a result, any standing water, such as a pool of water adjacent an ice dam, can leak under and between roof tiles into the building causing damage and/or promoting mold growth. Hot spots on a roof can develop where air stagnates between the roof deck and an underlying ceiling panel. Such hot spots often occur adjacent skylights. Typically, a skylight is installed on and between rafters. The installed skylight blocks natural convection in the space defined between the rafters. This causes the air between the rafters to become stagnated and overheated, thereby allowing formation of ice dams and resulting water damage. One technique that has been used to eliminate this problem is to drill holes through the rafters to allow air to flow around the skylight. However, this results in weakening of the structure and is extremely labor intensive. Therefore, there is a need for improved building techniques and structures that allow free convection around skylights.
A further problem with current building construction techniques is that they tend to allow toxic volatile organic compounds (VOCs) that are off-gassed from construction materials, such as flooring, paints, varnishes, cabinets, etc., to accumulate in living spaces and in spaces between exterior sheathing and interior walls. Toxic pollutants may continue to off-gas from various building materials for several years after they have been installed. Accumulation of these off-gassed VOCs in stagnate air between exterior sheathing and interior wall panels may significantly extend this period thereby increasing health risks. Accordingly, there is a need for improved construction techniques and building structures that enhance natural convection in the spaces between exterior sheathing and interior wall panels of buildings in order to minimize undesirable health risks associated with toxic compounds off-gassed from building materials.